Ozone Hole

Ozone hole
==========
Yesterday, we had a discussion on what an ozone hole is? Why do we always say that there is a hole over Antarctica? Is it because of the poles? If so, why don’t we talk about hole over the arctic pole?

Thanks to google, I found answers to some of them

How is the ozone hole created?

Each spring in the stratosphere over Antarctica (Spring in the southern hemisphere is from September through November.), atmospheric ozone is rapidly destroyed by chemical processes.

As winter arrives, a vortex of winds develops around the pole and isolates the polar stratosphere. When temperatures drop below -78°C (-109°F), thin clouds form of ice, nitric acid, and sulphuric acid mixtures. Chemical reactions on the surfaces of ice crystals in the clouds release active forms of CFCs. Ozone depletion begins, and the ozone “hole” appears.

Over the course of two to three months, approximately 50% of the total column amount of ozone in the atmosphere disappears. At some levels, the losses approach 90%. This has come to be called the Antarctic ozone hole.

In spring, temperatures begin to rise, the ice evaporates, and the ozone layer starts to recover.

British scientists Joesph Farman, Brian Gardiner, and Jonathan Shanklin of the British Antarctic Survey discovered the Antarctic ozone hole in 1985.

The ozone "hole" is really a reduction in concentrations of ozone high above the earth in the stratosphere. The ozone hole is defined geographically as the area wherein the total ozone amount is less than 220 Dobson Units. The ozone hole has steadily grown in size (up to 27 million sq. km.) and length of existence (from August through early December) over the past two decades.

Why is it concentrated over Antarctica?

As mid-May brings on the onset of winter, the Antarctic stratosphere cools and descends closer to the surface. The Coriolis effect (caused by the earths rotation) sets up a strong westerly circulation around the south pole, forming an oblong vortex which varies in size from year to year.

As temperatures in the lower stratosphere cools below -80'C, Polar Stratospheric Clouds (PSC's) start to form.

In the area over Antarctica, there are stratospheric cloud ice particles that are not present at warmer latitudes. Reactions occur on the surface of the ice particles that accelerate the ozone destruction caused by stratospheric chlorine. Polar regions get a much larger variation in sunlight than anywhere else, and during the 3 months of winter spend most of time in the dark without solar radiation. Temperatures hover around or below -80'C for much of the winter and the extremely low antarctic temperatures cause cloud formation in the relatively ''dry''stratosphere. These Polar Stratospheric Clouds (PSC's) are composed of ice crystals that provide the surface for a multitude of reactions, many of which speed the degredation of ozone molecules. This phenomenon has caused documented decreases in ozone concentrations over Antarctica.

In fact, ozone levels drop so low in spring in the Southern Hemisphere that scientists have observed what they call a "hole" in the ozone layer. The ozone destruction process requires conditions cold enough for stratospheric clouds to form. Once these stratospheric clouds form the process can take place, even in warmer conditions.

We do have ozone hole over the Arctic pole also.

Is Ozone really caused due to the emission of automobiles like our Chennai's pride MTC buses, Autos.....?

The Ozone Hole often gets confused in the popular press and by the general public with the problem of global warming. Whilst there is a connection because ozone contributes to the greenhouse effect, the Ozone Hole is a separate issue. However it is another stark reminder of the effect of man's activities on the environment.

Over Antarctica (and recently over the Arctic), stratospheric ozone has been depleted over the last 15 years at certain times of the year. This is mainly due to the release of manmade chemicals containing chlorine such as CFC's (ChloroFluoroCarbons), but also compounds containing bromine, other related halogen compounds and also nitrogen oxides (NOx). CFC's are a common industrial product, used in refrigeration systems, air conditioners, aerosols, solvents and in the production of some types of packaging. Nitrogen oxides are a by-product of combustion processes, eg aircraft emissions.

Courtesy

theozonehole

ozone hole